Shiitake is a mushroom belonging to Lentius genus of Agaricales Pleurotaceae family of Basidiomycetes. Shiitake is a wood-borne fungus that parasitizes in broad-leaved trees such as oak and beech trees in the temperate region from spring to autumn, and Shiitake grows alone or in clusters in a tree stump or a stump of a broad-leaved tree. Together with oyster mushrooms, Shiitake has been widely used for edible purposes for a long time, and is one of mushrooms that are grown actively in a commercial way due to artificial cultivation.
Shiitake is rich in various minerals and vitamins, and also contains fiber that helps digestion in stomach and small intestine. Thus, shiitake is good for obesity, diabetes, heart disease, and liver disease. Shiitake is also rich in protein, calcium, phosphorus, iron, vitamin D which helps bones be in a good shape, vitamin B that is essential for hematopoiesis, and ellatethene which helps blood metabolism. Sun-dried shiitake is about twice as nutritious as fresh shiitake. In particular, sun-dried shiitake is rich in vitamin D, which helps the absorption of calcium. In this aspect, shiitake strengthens teeth and prevents osteoporosis.
Vitamin D is an important nutrient that facilitates absorption of calcium and phosphate in the intestine, transfers calcium from the calcified skeleton to the blood, and helps calcium and phosphate to be re-absorbed by the kidney. Up to now, D2 to D7 have been found as vitamin D, and from among these, D2 and D3 are biologically active. Due to ultraviolet (UV) light irradiation, vitamin D2 (ergocalciferol) is synthesized from ergosterol that is plant sterol and vitamin D3 (cholecalciferol) is synthesized from cholesterol that is an animal sterol. Vitamin D synthesized as described above is converted into the active form of 1,25-dihydroxyvitamin D in the kidney via the liver, and 1,25-dihydroxyvitamin D promotes the synthesis of calcium-binding-proteins in the small intestine, thereby helping calcium to be absorbed. When the concentration of the active vitamin D is increased, the intestine absorbs more calcium, leading to a higher calcium concentration in the blood.
Since vitamin D is biosynthesized in the body when exposed to the sun, unlike other nutrients that need to be supplied only as food, vitamin D is considered as a less important nutrient. Recently, the use of various sunscreen products to block UV light limits the time for exposure to UV light, thereby hindering the biosynthesis of vitamin D in the skin. In particular, in the case of the menopausal women and the elderly, less exposure to UV light may mean an extreme limitation on the biosynthesis of vitamin D. Accordingly, the supply of vitamin D via the diet is inevitable. Vitamin D that can be ingested via diet is present in large amounts in mushrooms and fish, and in small amounts in egg yolks, milk and dairy products. However, not only limited number of foods provides vitamin D via diet, but the amount of vitamin D contained in such foods is very low. Accordingly, the supply of vitamin D via foods is very limited. In the United States, vitamin D-fortified foods, such as milk, dairy products, orange juice, and nutrition bars, are being sold to compensate for the lack of vitamin D. In Korea, vitamin D-fortified milk is commercially available, but there are only few vitamin D-fortified products. Therefore, there is a need to develop vitamin D-enriched foods.
Korean Patent No. 1168747 discloses a method of cultivating oyster mushrooms of which the ergosterol content is enhanced by LED illumination. However, the disclosed method is different from the method of obtaining vitamin D2 from shiitake mushrooms according to the present disclosure.